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Colosseum
Post subject: Re: Personal Design - Derry-class CAPosted: November 21st, 2017, 4:14 pm
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Looking good, I like the slow evolution of the class. I think by the time you reach the King Board refits you'd likely see gun #3 replaced with a second Mark 19 director platform. This also made me realize there's no after/emergency conn on this ship ("Battle 2"), and that would probably need to go just forward of mount #3. It would contain duplicated controls from the bridge (with very little weather protection) and serve as a backup conn in case the bridge was destroyed.

Looking forward to seeing how this ship would be refitted throughout the war. I imagine it would be similar to the Omaha class refits (to me this ship is sort of a "super Omaha"). That is, of course, if in your timeline this ship survives the early days of the Pacific. ;)

Great work.

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Krakatoa
Post subject: Re: Personal Design - Derry-class CAPosted: November 21st, 2017, 6:15 pm
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I like it.

Couple of points, that forebridge superstructure has added a lot of topweight to the ship. To balance it out, by 1940-41 you would probably have removed the torpedo tubes to help compensate. That was something all of the older cruisers had a problem with. All the additional electronics and AA weaponry added more topweight that needed to be compensated for. Once you add your radar and other stuff you may find you need to take off your highest 7" and the superstructure it sits on. It is a continual tradeoff. I am sure you will work it out.


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matedow
Post subject: Re: Personal Design - Derry-class CAPosted: November 24th, 2017, 1:50 pm
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Colosseum wrote: *
Looking good, I like the slow evolution of the class. I think by the time you reach the King Board refits you'd likely see gun #3 replaced with a second Mark 19 director platform. This also made me realize there's no after/emergency conn on this ship ("Battle 2"), and that would probably need to go just forward of mount #3. It would contain duplicated controls from the bridge (with very little weather protection) and serve as a backup conn in case the bridge was destroyed.
Ok, here are updated designs with after controls added, plus an after director as a part of the 1940 King Board improvements. No 1941 version yet because of the time it will take to correct the paint scheme.

[ img ]


[ img ]


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Looking forward to seeing how this ship would be refitted throughout the war. I imagine it would be similar to the Omaha class refits (to me this ship is sort of a "super Omaha"). That is, of course, if in your timeline this ship survives the early days of the Pacific. ;)
There will be some different designs, and I am sure that at least one of these ships would have been lost in the Solomons.

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Great work.
Thank you


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matedow
Post subject: Re: Personal Design - Derry-class CAPosted: November 24th, 2017, 2:04 pm
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Krakatoa wrote: *
I like it.

Couple of points, that forebridge superstructure has added a lot of topweight to the ship. To balance it out, by 1940-41 you would probably have removed the torpedo tubes to help compensate. That was something all of the older cruisers had a problem with. All the additional electronics and AA weaponry added more topweight that needed to be compensated for. Once you add your radar and other stuff you may find you need to take off your highest 7" and the superstructure it sits on. It is a continual tradeoff. I am sure you will work it out.
I don't have a feel for how accurately that Springsharp accounts for the stability effect of added weight. I added 50 tons of above deck miscellaneous weight to account for the added fire control equipment in the 1930 refit, and then an additional 20 tons for the 1940 version. This is in addition to the 150 tons of armor for the guns in the form of shields. This has resulted in a reduction of the metacentric height from 4.3 feet to 4.2 feet, and the draft increased by 0.5 feet with the attendant loss of range and speed.

Do you have the feeling that the stability calculations that Springsharp makes are accurate? Do I need additional miscellaneous weight to account for the superstructure and above deck components of the fire control systems?

With the assumption that the program is correct, in 1941 you don't have to make radical weight saving measures through removal of guns or superstructure... yet. With the addition of detection and fire control radars, in addition to the heavier AA batteries, that will obviously become necessary.

Does that sound accurate?


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matedow
Post subject: Re: Personal Design - Derry-class CAPosted: November 24th, 2017, 3:14 pm
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OK, here is the updated 1941 version...

[ img ]


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JSB
Post subject: Re: Personal Design - Derry-class CAPosted: November 25th, 2017, 6:25 pm
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matedow wrote: *
I don't have a feel for how accurately that Springsharp accounts for the stability effect of added weight.
I'm not sure that Spring Sharp work's well for modifications as it would assume that any sim is simply a new ships with different sizes, so it doesn't account for the wasted weight and lack of flexibility of a modification.


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Krakatoa
Post subject: Re: Personal Design - Derry-class CAPosted: November 25th, 2017, 7:44 pm
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I am not a good person to ask about Spring Sharp. I do not like the program at all. I feel it takes away peoples intelligence. By that I mean the ability to think for yourself. To actually go out and do by 'hand' the accruing of resources and references, from reading books, hunting online for obscure references and line drawings to base both your real and AU/PD drawings on, actually going out into the real world and looking at the museum ships and museums which hold lifetimes of facts contained in them. Learning what makes a ship tick without having to do an engineering course.

Pretty much makes me old school.

But... there are a lot of pixel artists in here that use SS to 'check' their drawings after they have drawn them. Not before they have drawn them. Most of the old time artists in here know that Spring Sharp is a very flawed program and do not rely on it.

A JSB said, each time you change something/anything in Spring Sharp, the program takes it as a new ship and sims it as such. With Spring Sharp you cannot tell the program the original 'real' ship was a flawed design to begin with. HMS Hood is a good example. In the real world we know the design was overloaded going from 36,000 tons to 42,000 tons and overstressing the hull. Spring Sharp has no way of entering that sort of data. Sim the Hood in SS and see what SS says about it.

Spring Sharp should be a very minor tool in your drawing process, not the driving force.

When building naval ships, all navies are building to budgets, whether it be money or materials or both. That means that each ship is going to be as good as it can be at the date that it is completed. Even though most navies expect those same ships to last in service 20-25 years and go through refit and rebuilding processes through those service years. The transition of WW1 to WW2 ships, like your Derry class, can be tremendous . All the navies remodelled their capital ships and cruisers. What was found was that whenever something was added, something else had to be removed to compensate. Everything is a trade off. If you want to add lots and not have to reduce armaments, then add bulges. That will have two effects, 1. slow your ship down due to the extra drag, 2. add some much needed anti-torpedo protection to your cruiser. That way you get a bit of leeway to add a bit more before having to remove armament.


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matedow
Post subject: Re: Personal Design - Derry-class CAPosted: November 26th, 2017, 7:03 am
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Krakatoa wrote: *
I am not a good person to ask about Spring Sharp. I do not like the program at all. I feel it takes away peoples intelligence. By that I mean the ability to think for yourself. To actually go out and do by 'hand' the accruing of resources and references, from reading books, hunting online for obscure references and line drawings to base both your real and AU/PD drawings on, actually going out into the real world and looking at the museum ships and museums which hold lifetimes of facts contained in them. Learning what makes a ship tick without having to do an engineering course.
Not everyone is going to have the knowledge or the resources to calculate hull stresses, machinery weight or the stability for a hypothetical design. I have a maritime background, so I'd like to think I do a decent job of creating "realistic" designs, but I also know that I look at things differently than the historical naval architects did.

For back of the envelope calculations, if I add 100 tons of weight 60 feet above the keel to a ship with a 10400 ton (normal load for Derry) displacement and an assumed KG of 9 feet (half normal draft which will put it near the center of buoyancy), it will raise the CG by approximately 0.5 feet. Springsharp doesn't tell me the KG that is uses, only the GM (metacentric height). The result matches the data that is presented in the program decently close; enough to suggest that I am getting a good estimation of how the changes to the design will effect the stability of the design. I don't have any way to check whether the calculations that it makes to derive the information originally are accurate. Of course, this is based on the assumption that the weight added would be approximately 100 tons, and I don't have historical data on the weight of the tripod mast and superstructure added versus the amount that I'd lose from removing the cage mast, hence an estimate on my part.

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Pretty much makes me old school.
I am too. That's why my wife is always telling me I have too many books and should just get a Kindle. ;)

Quote:
But... there are a lot of pixel artists in here that use SS to 'check' their drawings after they have drawn them. Not before they have drawn them. Most of the old time artists in here know that Spring Sharp is a very flawed program and do not rely on it.
Apparently I'm coming at it backwards. I had the designs in my head and used Springsharp to develop stats and make sure that I had made reasonable assumptions. Springsharp is a convenient way of "designing" a ship to fit the vision in my head of how a progression of ships should be. I know that it isn't ideal, but do try and conduct my own reality check on the numbers that it generates. I also accept that it tends to make post-1920 powerplants heavy for a particular power rating and not as efficient as the US plants were historically, but conservative numbers in those areas probably compensate for auxiliary equipment that isn't accounted for.

I did sketches based on those stats and now it is interesting to turn those black and white sketches into something that looks nice and represents what a "real" ship might have looked like.

Quote:
A JSB said, each time you change something/anything in Spring Sharp, the program takes it as a new ship and sims it as such. With Spring Sharp you cannot tell the program the original 'real' ship was a flawed design to begin with. HMS Hood is a good example. In the real world we know the design was overloaded going from 36,000 tons to 42,000 tons and overstressing the hull. Spring Sharp has no way of entering that sort of data. Sim the Hood in SS and see what SS says about it.
I had noticed that fact, but it seems to do better when you keep the years consistent within a design. It isn't a naval architect in a box, but it is the best that most people have access to.

Quote:
When building naval ships, all navies are building to budgets, whether it be money or materials or both. That means that each ship is going to be as good as it can be at the date that it is completed. Even though most navies expect those same ships to last in service 20-25 years and go through refit and rebuilding processes through those service years. The transition of WW1 to WW2 ships, like your Derry class, can be tremendous . All the navies remodelled their capital ships and cruisers. What was found was that whenever something was added, something else had to be removed to compensate. Everything is a trade off. If you want to add lots and not have to reduce armaments, then add bulges. That will have two effects, 1. slow your ship down due to the extra drag, 2. add some much needed anti-torpedo protection to your cruiser. That way you get a bit of leeway to add a bit more before having to remove armament.
Unlike many of the inter-war refits, the Derry isn't getting additional deck armor, converting from coal to oil, or other structural changes to the hull and powerplant. This reconstruction would be more similar to the changes to the US pre-dreadnought battleships when they exchanged their tubular masts for cage masts and added superstructure, or at least that was the model in my head when I was envisioning this refit.


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